Enhancement of survival of stored dopaminergic cells and promotion of graft survival by exposure of human fetal nigral tissue to glial cell line--derived neurotrophic factor in patients with Parkinson's disease. Report of two cases and technical considerations

Enhancement of endogenous midbrain neurogenesis by microneurotrophin BNN-20 after neural progenitor grafting in a mouse model of nigral degeneration

We have previously shown the neuroprotective and pro-neurogenic activity of microneurotrophin BNN-20 in the substantia nigra of the “weaver” mouse, a model of progressive nigrostriatal degeneration. Here, we extended our investigation in two clinically-relevant ways. First, we assessed the effects of BNN-20 on human induced pluripotent stem cell-derived neural progenitor cells and neurons derived from healthy and parkinsonian donors. Second, we assessed if BNN-20 can boost the outcome of mouse neural progenitor cell intranigral transplantations in weaver mice, at late stages of degeneration. We found that BNN-20 has limited direct effects on cultured human induced pluripotent stem cell-derived neural progenitor cells, marginally enhancing their differentiation towards neurons and partially reversing the pathological phenotype of dopaminergic neurons generated from parkinsonian donors. In agreement, we found no effects of BNN-20 on the mouse neural progenitor cells grafted in the substantia nigra of weaver mice. However, the graft strongly induced an endogenous neurogenic response throughout the midbrain, which was significantly enhanced by the administration of microneurotrophin BNN-20. Our results provide straightforward evidence of the existence of an endogenous midbrain neurogenic system that can be specifically strengthened by BNN-20. Interestingly, the lack of major similar activity on cultured human induced pluripotent stem cell-derived neural progenitors and their progeny reveals the in vivo specificity of the aforementioned pro-neurogenic effect.

Sarcosine May Induce EGF Production or Inhibit the Decline in EGF Concentrations in Patients with Chronic Schizophrenia (Results of the PULSAR Study)

Sarcosine (N-methylglycine), a glutamatergic modulator, reduces the primary negative symptoms of schizophrenia. These beneficial changes might be mediated by trophic factors such as epidermal growth factor (EGF). We assessed associations between initial serum EGF levels or changes in serum EGF levels and symptom severity during the addition of sarcosine to stable antipsychotic treatment and thereby evaluated the associations between glutamatergic modulation, clinical changes and peripheral EGF concentrations. Fifty-eight subjects with a diagnosis of chronic schizophrenia with dominant negative symptoms, stably treated with antipsychotics, completed a prospective 6-month, randomized, double-blind, placebo-controlled study. Subjects received orally 2 g of sarcosine (n = 28) or placebo (n = 30) daily. Serum EGF levels and symptom severity (using the Positive and Negative Syndrome Scale (PANSS) and the Calgary Depression Scale for Schizophrenia (CDSS)) were assessed at baseline, 6-week and 6-month follow-up. Augmentation antipsychotic treatment with sarcosine had no effect on EGF serum levels at any time points. Only the sarcosine group showed a significant improvement in negative symptoms, general psychopathology subscales and the overall PANSS score. We found a reduction in serum EGF levels in the placebo group, but levels in the sarcosine remained stable during the study. Our data indicate that improvement in negative symptoms due to sarcosine augmentation is not directly mediated by EGF, but effective treatment may induce the production or block the decrease in EGF concentrations, which indicates the neuroprotective effect of treatment and confirms the relationship between neuroprotection and EGF levels.

Cell-therapy for Parkinson's disease: a systematic review and meta-analysis

BACKGROUND

Cell-based strategies focusing on replacement or protection of dopaminergic neurons have been considered as a potential approach to treat Parkinson's disease (PD) for decades. However, despite promising preclinical results, clinical trials on cell-therapy for PD reported mixed outcomes and a thorough synthesis of these findings is lacking. We performed a systematic review and meta-analysis to evaluate cell-therapy for PD patients.

METHODS

We systematically identified all clinical trials investigating cell- or tissue-based therapies for PD published before July 2023. Out of those, studies reporting transplantation of homogenous cells (containing one cell type) were included in meta-analysis. The mean difference or standardized mean difference in quantitative neurological scale scores before and after cell-therapy was analyzed to evaluate treatment effects.

RESULTS

The systematic literature search revealed 106 articles. Eleven studies reporting data from 11 independent trials (210 patients) were eligible for meta-analysis. Disease severity and motor function evaluation indicated beneficial effects of homogenous cell-therapy in the 'off' state at 3-, 6-, 12-, or 24-month follow-ups, and for motor function even after 36 months. Most of the patients were levodopa responders (61.6-100% in different follow-ups). Cell-therapy was also effective in improving the daily living activities in the 'off' state of PD patients. Cells from diverse sources were used and multiple transplantation modes were applied. Autografts did not improve functional outcomes, while allografts exhibited beneficial effects. Encouragingly, both transplantation into basal ganglia and to areas outside the basal ganglia were effective to reduce disease severity. Some trials reported adverse events potentially related to the surgical procedure. One confirmed and four possible cases of graft-induced dyskinesia were reported in two trials included in this meta-analysis.

CONCLUSIONS

This meta-analysis provides preliminary evidence for the beneficial effects of homogenous cell-therapy for PD, potentially to the levodopa responders. Allogeneic cells were superior to autologous cells, and the effective transplantation sites are not limited to the basal ganglia. PROSPERO registration number: CRD42022369760.

Clinical considerations in Parkinson's disease cell therapy

Cell replacement therapy is an area of increasing interest for treating Parkinson's disease (PD). However, to become a clinically practical option for PD patients, it must first overcome significant barriers, including establishment of safe and standardized surgical procedures, determination of appropriate perioperative medication regimens, demonstration of long-term graft survival and incorporation, and standardized, clinically meaningful follow-up measures. In this review, we will describe the current status of cell therapy for PD with special attention to these critical requirements, to define guideposts on the road to bring the benefit of this therapy to the Parkinson's clinic.

Gene Therapy in the Management of Parkinson's Disease: Potential of GDNF as a Promising Therapeutic Strategy

The limitations of conventional treatment therapies in Parkinson's disorder, a common neurodegenerative disorder, lead to the development of an alternative gene therapy approach. Multiple treatment options targeting dopaminergic neuronal regeneration, production of enzymes linked with dopamine synthesis, subthalamic nucleus neurons, regulation of astrocytes and microglial cells and potentiating neurotrophic factors, were established. Viral vector-based dopamine delivery, prodrug approaches, fetal ventral mesencephalon tissue transplantation and dopamine synthesizing enzyme encoding gene delivery are significant therapies evidently supported by numerous trials. The review primarily elaborates on the significant role of glial cell-line derived neurotrophic factor in alleviating motor symptoms and the loss of dopaminergic neurons in Parkinson's disease. Neuroprotective and neuroregenerative effects of GDNF were established via preclinical and clinical study outcomes. The binding of GDNF family ligands with associated receptors leads to the formation of a receptor-ligand complex activating Ret receptor of tyrosine kinase family, which is only expressed in dopaminergic neurons, playing an important role in Parkinson's disease, via its association with the essential protein encoded genes. Furthermore, the review establishes delivery aspects, like ventricular delivery of recombinant GDNF, intraparenchymal and intraputaminal delivery using infusion catheters. The review highlights problems and challenges of GDNF delivery, and essential measures to overcome them, like gene therapy combinations, optimization of delivery vectors, newer targeting devices, motor symptoms curbing focused ultrasound techniques, modifications in patient selection criteria and development of novel delivery strategies based on liposomes and encapsulated cells, to promote safe and effective delivery of neurotrophic factor and establishment of routine treatment therapy for patients.

Postmortem Studies of Fetal Grafts in Parkinson's Disease: What Lessons Have We Learned?

Neural transplantation is a potential therapeutic method for Parkinson’s disease (PD). Fetal dopaminergic (DA) neurons have been important transplantation cell sources in the history of replacement therapy for PD. Several decades of preclinical animal experiments and clinical trials using fetal DA neuron transplantation in PD therapy have shown not only promising results but also problems. In order to reveal possible factors influencing the clinical outcomes, we reviewed fetal DA neuron transplantation therapies from 1970s to present, with a special focus on postmortem studies. Firstly, we gave a general description of the clinical outcomes and neuroanatomy of grafted cases; secondly, we summarized the main available postmortem studies, including the cell survival, reinnervation, and pathology development. In the end, we further discussed the link between function and structure of the grafts, seeking for the possible factors contributing to a functional graft. With our review, we hope to provide references for future transplantation trials from a histological point of view.

Is the Immunological Response a Bottleneck for Cell Therapy in Neurodegenerative Diseases?

Neurodegenerative disorders such as Parkinson's (PD) and Huntington's disease (HD) are characterized by a selective detrimental impact on neurons in a specific brain area. Currently, these diseases have no cures, although some promising trials of therapies that may be able to slow the loss of brain cells are underway. Cell therapy is distinguished by its potential to replace cells to compensate for those lost to the degenerative process and has shown a great potential to replace degenerated neurons in animal models and in clinical trials in PD and HD patients. Fetal-derived neural progenitor cells, embryonic stem cells or induced pluripotent stem cells are the main cell sources that have been tested in cell therapy approaches. Furthermore, new strategies are emerging, such as the use of adult stem cells, encapsulated cell lines releasing trophic factors or cell-free products, containing an enriched secretome, which have shown beneficial preclinical outcomes. One of the major challenges for these potential new treatments is to overcome the host immune response to the transplanted cells. Immune rejection can cause significant alterations in transplanted and endogenous tissue and requires immunosuppressive drugs that may produce adverse effects. T-, B-lymphocytes and microglia have been recognized as the main effectors in striatal graft rejection. This review aims to summarize the preclinical and clinical studies of cell therapies in PD and HD. In addition, the precautions and strategies to ensure the highest quality of cell grafts, the lowest risk during transplantation and the reduction of a possible immune rejection will be outlined. Altogether, the wide-ranging possibilities of advanced therapy medicinal products (ATMPs) could make therapeutic treatment of these incurable diseases possible in the near future.

Neurotrophic factor-based strategies to enhance survival and differentiation of neural progenitor cells toward the dopaminergic phenotype

Parkinson's disease (PD) is a neurodegenerative disorder that presents with hallmark clinical symptoms of tremor at rest, bradykinesia, and muscle rigidity. Stem cell therapy has emerged as an experimental treatment for PD. However, optimizing the cell culture condition that allows enhanced survival and differentiation of cells toward the dopaminergic phenotype remains a logistical challenge. Here, we discuss the utility of a combination of neurotrophin-4/5 (NT-4/5) and glial cell line-derived neurotrophic factor (GDNF) in increasing the dopaminergic phenotypic expression of rat ventral mesencephalic (VM) tissue. Using organotypic explant cultures of fetal human ventral mesencephalon, we observed that NT-4/5 and GDNF as single factors, or in combination on DAergic neurons, increased survival and number of tyrosine hydroxylase immunoreactive neurons as well as the dopamine content in the culture medium. The application of specific neurotrophic factors, such as NT-4/5 and GDNF, as cell culture supplements or as adjunctive therapy to cell transplantation may achieve improved functional outcomes when contemplating cell-based regenerative medicine for PD.

Combination of cell transplantation and glial cell line-derived neurotrophic factor-secreting encapsulated cells in Parkinson's disease

A major limitation of cell transplantation for Parkinson's disease (PD) is the mediocre survival of the grafted cells. Facilitating graft survival may improve the functional outcomes of the transplanted cells. Here, we discuss our observations that combination of rat fetal ventral mesencephalic (VM) tissue and encapsulated cells that secrete glial cell line-derived neurotrophic factor (GDNF) enhanced graft function in an animal model of PD. We described significant 2-fold increase in the number of tyrosine hydroxylase immunoreactive (TH-ir) cells per graft, as well as 1.7-fold and 9-fold increments in TH-ir fiber outgrowth into the host brain and toward the capsule with combined transplants and GDNF capsules as opposed to the VM transplants and mock-capsule group. These findings demonstrate that encapsulated GDNF-secreting cells improve graft survival that may optimize functional benefits for the treatment of PD.

Emerging Treatment Approaches for Parkinson's Disease

Parkinson’s disease (PD) is the second most common neurodegenerative disease, manifesting as a characteristic movement disorder with a number of additional non-motor features. The pathological hallmark of PD is the presence of intra-neuronal aggregates of α-synuclein (Lewy bodies). The movement disorder of PD occurs largely due to loss of dopaminergic neurons of the substantia nigra, resulting in striatal dopamine depletion. There are currently no proven disease modifying treatments for PD, with management options consisting mainly of dopaminergic drugs, and in a limited number of patients, deep brain stimulation. Long-term use of established dopaminergic therapies for PD results in significant adverse effects, and there is therefore a requirement to develop better means of restoring striatal dopamine, as well as treatments that are able to slow progression of the disease. A number of exciting treatments have yielded promising results in pre-clinical and early clinical trials, and it now seems likely that the landscape for the management of PD will change dramatically in the short to medium term future. Here, we discuss the promising regenerative cell-based and gene therapies, designed to treat the dopaminergic aspects of PD whilst limiting adverse effects, as well as novel approaches to reducing α-synuclein pathology.

Cell-based therapy for Parkinson's disease: A journey through decades toward the light side of the Force

This review describes the history, development, and evolution of cell‐based replacement therapy for Parkinson's disease (PD), from the first pioneering trials with fetal ventral midbrain progenitors to future trials using stem cells as well as reprogrammed cells. In the spirit of Tom Isaacs, the review takes parallels to the storyline of Star Wars, including the temptations from the dark side and the continuous fight for the light side of the Force. It is subdivided into headings based on the original movies, spanning from A New Hope to the Last Jedi.

Simultaneous Transplantation of Fetal Ventral Mesencephalic Tissue and Encapsulated Genetically Modified Cells Releasing GDNF in a Hemi-Parkinsonian Rat Model of Parkinson's Disease

Transplantation of fetal ventral mesencephalic (VM) neurons for Parkinson’s disease (PD) is limited by poor survival and suboptimal integration of grafted tissue into the host brain. In a 6-hydroxydopamine rat model of PD, we investigated the feasibility of simultaneous transplantation of rat fetal VM tissue and polymer-encapsulated C2C12 myoblasts genetically modified to produce glial cell line–derived neurotrophic factor (GDNF) or mock-transfected myoblasts on graft function. Amphetamine-induced rotations were assessed prior to transplantation and 2, 4, 6 and 9 wk posttransplantation. We found that rats grafted with VM transplants and GDNF capsules showed a significant functional recovery 4 wk after implantation. In contrast, rats from the VM transplant and mock-capsule group did not improve at any time point analyzed. Moreover, we detected a significantly higher number of tyrosine hydroxylase immunoreactive (TH-ir) cells per graft (2-fold), a tendency for a larger graft volume and an overall higher TH-ir fiber outgrowth into the host brain (1.7-fold) in the group with VM transplants and GDNF capsules as compared to the VM transplant and mock-capsule group. Most prominent was the TH-ir fiber outgrowth toward the capsule (9-fold). Grafting of GDNF-pretreated VM transplants in combination with the implantation of GDNF capsules resulted in a tendency for a higher TH-ir fiber outgrowth into the host brain (1.7-fold) as compared to the group transplanted with untreated VM transplants and GDNF capsules. No differences between groups were observed for the number of surviving TH-ir neurons or graft volume. In conclusion, our findings demonstrate that simultaneous transplantation of fetal VM tissue and encapsulated GDNF-releasing cells is feasible and support the graft survival and function. Pretreatment of donor tissue with GDNF may offer a way to further improve cell transplantation approaches for PD.

A Combination of NT-4/5 and GDNF Is Favorable for Cultured Human Nigral Neural Progenitor Cells

Idiopathic Parkinson’s disease (PD) is a progressive neurodegenerative disorder, clinically manifested by cardinal motor symptoms including tremor at rest, bradykinesia, and muscle rigidity. Transplantation of dopaminergic (DAergic) neurons is an experimental therapy for PD, however, it is limited by suboptimal integration and low survival of grafts. Pretreatment of donor tissue may offer a strategy to improve properties of transplanted DAergic neurons and thereby clinical outcome. We have previously shown that a combination of neurotrophin-4/5 (NT-4/5) and glial cell line-derived neurotrophic factor (GDNF) demonstrated additive effects on rat ventral mesencephalic (VM) tissue. The present study investigated the effects of NT-4/5 and GDNF as single factors, or in combination on DAergic neurons, in organotypic explant cultures of fetal human ventral mesencephalon. For that purpose, free-floating roller-tube cultures were prepared from VM and the equally sized pieces grown for 1 week in the presence or absence of neurotrophic factors. Both neurotrophic factors increased dopamine content in the culture medium and in the number of tyrosine hydroxylase immunoreactive neurons, most prominently after combined GDNF + NT-4/5 treatment. Culture volumes did not differ between groups while content of lactate dehydrogenase in the culture medium was moderately reduced in all treated groups. In conclusion, we identified that a combination of GDNF and NT-4/5 robustly promoted differentiation and survival of human fetal VM DAergic neurons, an observation with potential promising impact for cell replacement approaches in PD.

Intermittent, low dose carbon monoxide exposure enhances survival and dopaminergic differentiation of human neural stem cells

Exploratory studies using human fetal tissue have suggested that intrastriatal transplantation of dopaminergic neurons may become a future treatment for patients with Parkinson's disease. However, the use of human fetal tissue is compromised by ethical, regulatory and practical concerns. Human stem cells constitute an alternative source of cells for transplantation in Parkinson's disease, but efficient protocols for controlled dopaminergic differentiation need to be developed. Short-term, low-level carbon monoxide (CO) exposure has been shown to affect signaling in several tissues, resulting in both protection and generation of reactive oxygen species. The present study investigated the effect of CO produced by a novel CO-releasing molecule on dopaminergic differentiation of human neural stem cells. Short-term exposure to 25 ppm CO at days 0 and 4 significantly increased the relative content of β-tubulin III-immunoreactive immature neurons and tyrosine hydroxylase expressing catecholaminergic neurons, as assessed 6 days after differentiation. Also the number of microtubule associated protein 2-positive mature neurons had increased significantly. Moreover, the content of apoptotic cells (Caspase3) was reduced, whereas the expression of a cell proliferation marker (Ki67) was left unchanged. Increased expression of hypoxia inducible factor-1α and production of reactive oxygen species (ROS) in cultures exposed to CO may suggest a mechanism involving mitochondrial alterations and generation of ROS. In conclusion, the present procedure using controlled, short-term CO exposure allows efficient dopaminergic differentiation of human neural stem cells at low cost and may as such be useful for derivation of cells for experimental studies and future development of donor cells for transplantation in Parkinson's disease.

Alterations of DNA Methylation at GDNF Gene Promoter in the Ventral Tegmental Area of Adult Depression-Like Rats Induced by Maternal Deprivation

Objective: To study the expression and DNA methylation of the Glial cell line-derived neurotrophic factor (GDNF) gene in the development of depression-like behaviors in rats experiencing maternal deprivation stress in early life. Methods: Newborn SD rats were randomly assigned to a normal control group (NOR) or maternal deprivation group (MD). An open field test (OPT), sucrose preference test (SPT), and a forced swimming test (FST) were used to evaluate rats' behaviors. Protein, mRNA, and methylation levels were measured by ELISA/Western blot, real-time PCR, and BiSulfte Amplicon sequencing PCR, respectively. Results: MD rats had significantly shorter total distance and more fecal pellets in OPT, a lower sucrose preference rate in SPT, and a longer immobility time in FST than NOR rats. Compared with NOR rats, MD rats showed a significantly higher plasma corticosterone (CORT) level. The levels of plasma dopamine (DA) and the GDNF were significantly lower in the MD rats than in NOR rats. In the ventral tegmental area (VTA) tissues, MD rats had a significantly higher level of methylation at the GDNF gene promoter than NOR rats. The expression of the GDNF mRNA and protein were significantly lower in MD rats than in NOR rats. The total distance was significantly correlated with plasma DA and GDNF, the DNA methylation level at the GDNF promoter and the GDNF mRNA level in the VTA. Fecal pellets showed a significant correlation with plasma CORT. The sucrose preference rate was significantly correlated with plasma DA, the DNA methylation level at the GDNF promoter and the GDNF mRNA level in the VTA. Immobility time showed a significant correlation with the plasma DA, the plasma GDNF and the GDNF mRNA level in the VTA. Conclusion: up-regulation of DNA methylation at the GDNF gene promotor and the subsequent down-regulation of the GDNF gene expression in the VTA, may be involved in the development of depression-like behaviors in rats experiencing MD in early life.

A Sequential Intrastriatal Dopaminergic Graft Strategy in the Rodent Model for Parkinson's Disease: Implications for Graft Survival and Targeting

Optimal placement of intrastriatal dopaminergic grafts is likely crucial to optimize clinical recovery in Parkinson's disease (PD). The target sites of dopaminergic grafts vary among clinical trials and may partially explain the variable results in clinical efficacy reported thus far. In this study we hypothesized that a subsequent dopaminergic graft may promote functional recovery following a suboptimal initial graft. To test this hypothesis, rats with unilateral 6-hydroxydopamine lesions of the right nigrostriatal pathway were randomly divided into three groups. The first group received 900,000 fetal nigral cells in the medial striatum only (n = 6). The second group received 900,000 cells in both the medial and lateral striatum simultaneously (1.8 million total; n = 8). The final group received a second graft of 900,000 cells in the lateral striatum 6 weeks following initial transplantation of a medial graft (n = 6). Amphetamine-induced circling behavior was significantly reduced in both simultaneous and sequential graft groups at 9 and 12 weeks following transplantation of the initial graft. However, no recovery was noted in the single medial graft group at those time points. Furthermore, increased survival of dopaminergic cells was observed in the lateral graft of sequentially grafted animals compared with the medial graft. We conclude that a well-positioned subsequent graft can restore function in animals with a suboptimal initial graft and that the initial graft may improve survival of the second graft. These results are further discussed in relation to their important clinical implication for neural transplantation in PD.

Quantitative [18F]Fluorodopa/PET and Histology of Fetal Mesencephalic Dopaminergic Grafts to the Striatum of MPTP-Poisoned Minipigs

The functional restoration of the dopamine innervation of striatum in MPTP-poisoned Göttingen minipigs was assessed for 6 months following grafting of fetal pig mesencephalic neurons. Pigs were assigned to a normal control group and a MPTP-poisoned group, members of which received no further treatment, or which received bilateral grafts to the striatum of tissue blocks harvested from E28 fetal pig mesencephalon with and without immunosuppressive treatment after grafting, or with additional co-grafting with immortalized rat neural cells transfected to produce GDNF. In the baseline condition, and again at 3 and 6 months postsurgery, all animals were subjected to quantitative [18F]fluorodopa PET scans and testing for motor impairment. At the end of 6 months, tyrosine hydroxylase (TH)-containing neurons were counted in the grafts by stereological methods. The MPTP poisoning persistently reduced the magnitude of k3D, the relative activity of DOPA decarboxylase in striatum, by 60%. Grafting restored the rate of [18F]fluorodopa decarboxylation to the normal range, and normalized the scores in motor function. The biochemical and functional recovery was associated with survival of approximately 100,000 TH-positive graft neurons in each hemisphere. Immunosuppression did not impart a greater recovery of [18F]fluorodopa uptake, nor were the number of TH-positive graft neurons or the volumes of the grafts increased in the immunosuppressed group. Contrary to expectation, co-grafting of transfected GDNF-expressing HiB5 cells, a rat-derived neural cell line, tended to impair the survival of the grafts with the lowest values for graft volumes, TH-positive cell numbers, behavioral scores, and relative DOPA decarboxylase activity. From the results we conclude that pig ventral mesencephalic allografts can restore functional dopamine innervation in adult MPTP-lesioned minipigs.

Cell Therapy for Parkinson's Disease

In Parkinson’s disease (PD), dopamine neurons in the substantia nigra are degenerated and lost. Cell therapy for PD replaces the lost dopamine neurons by transplanting donor dopamine neural progenitor cells. Cell therapy for PD has been performed in the clinic since the 1980s and uses donor cells from the mesencephalon of aborted embryos. Regenerative medicine for PD using induced pluripotent stem (iPS) cell technology is drawing attention, because it offers a limitless and more advantageous source of donor cells than aborted embryos.

Merging DBS with viral vector or stem cell implantation: "hybrid" stereotactic surgery as an evolution in the surgical treatment of Parkinson's disease

Parkinson’s disease (PD) is a complex neurodegenerative disorder that is currently managed using a broad array of symptom-based strategies. However, targeting its molecular origins represents the potential to discover disease-modifying therapies. Deep brain stimulation (DBS), a highly successful treatment modality for PD symptoms, addresses errant electrophysiological signaling pathways in the basal ganglia. In contrast, ongoing clinical trials testing gene and cell replacement therapies propose to protect or restore neuronal-based physiologic dopamine transmission in the striatum. Given promising new platforms to enhance target localization—such as interventional MRI-guided stereotaxy—the opportunity now exists to create hybrid therapies that combine DBS with gene therapy and/or cell implantation. In this mini-review, we discuss approaches used for central nervous system biologic delivery in PD patients in previous trials and propose a new set of strategies based on novel molecular targets. A multifaceted approach, if successful, may not only contribute to our understanding of PD pathology but could introduce a new era of disease modification.

Cell-based therapies for Parkinson disease—past insights and future potential

Parkinson disease (PD) is characterized by loss of the A9 nigral neurons that provide dopaminergic innervation to the striatum. This discovery led to the successful instigation of dopaminergic drug treatments in the 1960s, although these drugs were soon recognized to lose some of their efficacy and generate their own adverse effects over time. Despite the fact that PD is now known to have extensive non-nigral pathology with a wide range of clinical features, dopaminergic drug therapies are still the mainstay of therapy, and work well for many years. Given the success of pharmacological dopamine replacement, pursuit of cell-based dopamine replacement strategies seemed to be the next logical step, and studies were initiated over 30 years ago to explore the possibility of dopaminergic cell transplantation. In this Review, we outline the history of this therapeutic approach to PD and highlight the lessons that we have learned en route. We discuss how the best clinical outcomes have been obtained with fetal ventral mesencephalic allografts, while acknowledging inconsistencies in the results owing to problems in trial design, patient selection, tissue preparation, and immunotherapy used post-grafting. We conclude by discussing the challenges of bringing the new generation of stem cell-derived dopamine cells to the clinic.

GDNF-based therapies, GDNF-producing interneurons, and trophic support of the dopaminergic nigrostriatal pathway. Implications for Parkinson's disease

The glial cell line-derived neurotrophic factor (GDNF) is a well-established trophic agent for dopaminergic (DA) neurons in vitro and in vivo. GDNF is necessary for maintenance of neuronal morphological and neurochemical phenotype and protects DA neurons from toxic damage. Numerous studies on animal models of Parkinson’s disease (PD) have reported beneficial effects of GDNF on nigrostriatal DA neuron survival. However, translation of these observations to the clinical setting has been hampered so far by side effects associated with the chronic continuous intra-striatal infusion of recombinant GDNF. In addition, double blind and placebo-controlled clinical trials have not reported any clinically relevant effect of GDNF on PD patients. In the past few years, experiments with conditional Gdnf knockout mice have suggested that GDNF is necessary for maintenance of DA neurons in adulthood. In parallel, new methodologies for exogenous GDNF delivery have been developed. Recently, it has been shown that a small population of scattered, electrically interconnected, parvalbumin positive (PV+) GABAergic interneurons is responsible for most of the GDNF produced in the rodent striatum. In addition, cholinergic striatal interneurons appear to be also involved in the modulation of striatal GDNF. In this review, we summarize current knowledge on brain GDNF delivery, homeostasis, and its effects on nigrostriatal DA neurons. Special attention is paid to the therapeutic potential of endogenous GDNF stimulation in PD.

Tricyclic antidepressant treatment evokes regional changes in neurotrophic factors over time within the intact and degenerating nigrostriatal system

In addition to alleviating depression, trophic responses produced by antidepressants may regulate neural plasticity in the diseased brain, which not only provides symptomatic benefit but also potentially slows the rate of disease progression in Parkinson's disease (PD). Recent in vitro and in vivo data provide evidence that neurotrophic factors such as brain-derived neurotrophic factor (BDNF) and glial cell line-derived neurotrophic factor (GDNF) may be key mediators of the therapeutic response to antidepressants. As such, we conducted a cross-sectional time-course study to determine whether antidepressant-mediated changes in neurotrophic factors occur in relevant brain regions in response to amitriptyline (AMI) treatment before and after intrastriatal 6-hydroxydopamine (6OHDA). Adult male Wistar rats were divided into seven cohorts and given daily injections (i.p.) of AMI (5mg/kg) or saline throughout the duration of the study. In parallel, various cohorts of intact or parkinsonian animals were sacrificed at specific time points to determine the impact of AMI treatment on trophic factor levels in the intact and degenerating nigrostriatal system. The left and right hemispheres of the substantia nigra, striatum, frontal cortex, piriform cortex, hippocampus, and anterior cingulate cortex were dissected, and BDNF and GDNF levels were measured with ELISA. Results show that chronic AMI treatment elicits effects in multiple brain regions and differentially regulates levels of BDNF and GDNF depending on the region. Additionally, AMI halts the progressive degeneration of dopamine (DA) neurons elicited by an intrastriatal 6-OHDA lesion. Taken together, these results suggest that AMI treatment elicits significant trophic changes important to DA neuron survival within both the intact and degenerating nigrostriatal system.

Challenges and promises in the development of neurotrophic factor-based therapies for Parkinson's disease

Parkinson's disease (PD) is a chronic movement disorder typically coupled to progressive degeneration of dopaminergic neurons in the substantia nigra (SN). The treatments currently available are satisfactory for symptomatic management, but the efficacy tends to decrease as neuronal loss progresses. Neurotrophic factors (NTFs) are endogenous proteins known to promote neuronal survival, even in degenerating states. Therefore, the use of these factors is regarded as a possible therapeutic approach, which would aim to prevent PD or to even restore homeostasis in neurodegenerative disorders. Intriguingly, although favorable results in in vitro and in vivo models of the disease were attained, clinical trials using these molecules have failed to demonstrate a clear therapeutic benefit. Therefore, the development of animal models that more closely reproduce the mechanisms known to underlie PD-related neurodegeneration would be a major step towards improving the capacity to predict the clinical usefulness of a given NTF-based approach in the experimental setting. Moreover, some adjustments to the design of clinical trials ought to be considered, which include recruiting patients in the initial stages of the disease, improving the efficacy of the delivery methods, and combining synergetic NTFs or adding NTF-boosting drugs to the already available pharmacological approaches. Despite the drawbacks on the road to the use of NTFs as pharmacological tools for PD, very relevant achievements have been reached. In this article, we review the current status of the potential relevance of NTFs for treating PD, taking into consideration experimental evidence, human observational studies, and data from clinical trials.

Serum and supplement optimization for EU GMP-compliance in cardiospheres cell culture

Cardiac progenitor cells (CPCs) isolated as cardiospheres (CSs) and CS-derived cells (CDCs) are a promising tool for cardiac cell therapy in heart failure patients, having CDCs already been used in a phase I/II clinical trial. Culture standardization according to Good Manufacturing Practices (GMPs) is a mandatory step for clinical translation. One of the main issues raised is the use of xenogenic additives (e.g. FBS, foetal bovine serum) in cell culture media, which carries the risk of contamination with infectious viral/prion agents, and the possible induction of immunizing effects in the final recipient. In this study, B27 supplement and sera requirements to comply with European GMPs were investigated in CSs and CDCs cultures, in terms of process yield/efficiency and final cell product gene expression levels, as well as phenotype. B27- free CS cultures produced a significantly reduced yield and a 10-fold drop in c-kit expression levels versus B27+ media. Moreover, autologous human serum (aHS) and two different commercially available GMP AB HSs were compared with standard research-grade FBS. CPCs from all HSs explants had reduced growth rate, assumed a senescent-like morphology with time in culture, and/or displayed a significant shift towards the endothelial phenotype. Among three different GMP gamma-irradiated FBSs (giFBSs) tested, two provided unsatisfactory cell yields, while one performed optimally, in terms of CPCs yield/phenotype. In conclusion, the use of HSs for the isolation and expansion of CSs/CDCs has to be excluded because of altered proliferation and/or commitment, while media supplemented with B27 and the selected giFBS allows successful EU GMP-complying CPCs culture.

Central nervous system stem cell transplantation for children with neuronal ceroid lipofuscinosis

OBJECT

Infantile and late-infantile neuronal ceroid lipofuscinoses (NCLs) are invariably fatal lysosomal storage diseases associated with defects in lysosomal enzyme palmitoyl-protein thioesterase 1 (PPT-1) or tripeptidyl peptidase 1 (TPP1) activity. Previous preclinical studies have demonstrated that human CNS stem cells (HuCNS-SCs) produce both PPT-1 and TPP1 and result in donor cell engraftment and reduced accumulation of storage material in the brain when tested in an NCL mouse model.

METHODS

HuCNS-SC transplantation was tested in an open-label dose-escalation Phase I clinical trial as a potential treatment for infantile and late-infantile NCL. Study design included direct neurosurgical transplantation of allogeneic HuCNS-SCs into the cerebral hemispheres and lateral ventricles accompanied by 12 months of immunosuppression.

RESULTS

Six children with either the infantile or late-infantile forms of NCL underwent low- (3 patients) and high- (3 patients) dose transplantation of HuCNS-SCs followed by immunosuppression. The surgery, immunosuppression, and cell transplantation were well tolerated. Adverse events following transplantation were consistent with the underlying disease, and none were directly attributed to the donor cells. Observations regarding efficacy of the intervention were limited by the enrollment criteria requiring that patients be in advanced stages of disease.

CONCLUSIONS

This study represents the first-in-human clinical trial involving transplantation of a purified population of human neural stem cells for a neurodegenerative disorder. The feasibility of this approach and absence of transplantation-related serious adverse events support further exploration of HuCNS-SC transplantation as a potential treatment for select subtypes of NCL, and possibly for other neurodegenerative disorders.

Neural tissue transplantation, repair, and rehabilitation

Transplants of cells and tissues to the central nervous system of adult mammals can, under appropriate conditions, survive, integrate, and function. In particular, the grafted cells can sustain functional recovery in animal models of a range of neurodegenerative conditions including genetic and idiopathic neurodegenerative diseases of adulthood and aging, ischemic stroke, and brain and spinal cord trauma. In a restricted subset of such conditions, cell transplantation has progressed to application in humans in early-stage clinical trials. At the present stage of play, there is clear evidence of clinical efficacy of fetal cell transplants in Parkinson disease (notwithstanding a range of technical difficulties still to be fully resolved), and preliminary claims of promising outcomes in several other severe neurodegenerative conditions, including Huntington disease and stroke. Moreover, the experimental literature is increasingly suggesting that the experience and training of the graft recipient materially affects the functional outcome. For example, environmental enrichment, behavioral activity, and specific training can enhance the recovery process to maximize functional recovery. There are even circumstances where the grafted cells have been demonstrated to restore the neural substrate for new learning. Consequently, it is not sufficient to replace lost cells anatomically; rather, for the grafts to be effective, they need to be integrated functionally into the host circuitry, and the host animal requires training and rehabilitation to maximize function of the reconstructed graft-host circuitry. Such observations require reconsideration of the design of the next generation of clinical trials and subsequent service delivery, to include physiotherapists, cognitive therapists, and rehabilitation experts as core members of the transplant team, along with the neurologists and neurosurgeons that have conventionally led the field.

PTEN deletion enhances survival, neurite outgrowth and function of dopamine neuron grafts to MitoPark mice

Clinical trials in Parkinson’s disease have shown that transplants of embryonic mesencephalic dopamine neurons form new functional connections within the host striatum, but the therapeutic benefits have been highly variable. One obstacle has been poor survival and integration of grafted dopamine neurons. Activation of Akt, a serine/threonine kinase that promotes cell survival and growth, increases the ability of neurons to survive after injury and to regenerate lost neuronal connections. Because the lipid phosphatase, phosphatase and tensin homolog (PTEN) inhibits Akt, we generated a mouse with conditional knock-out of PTEN in dopamine neurons, leading to constitutive expression of Akt in these neurons. Ventral mesencephalic tissue from dopamine phosphatase and tensin homologue knock-out or control animals was then transplanted bilaterally into the dopamine depleted striata of MitoPark mice that express a parkinsonian phenotype because of severe respiratory chain dysfunction in dopamine neurons. After transplantation into MitoPark mice, PTEN-deficient dopamine neurons were less susceptible to cell death, and exhibited a more extensive pattern of fibre outgrowth compared to control grafts. Voltammetric measurements demonstrated that dopamine release and reuptake were significantly increased in the striata of animals receiving dopamine PTEN knock-out transplants. These animals also displayed enhanced spontaneous and drug-induced locomotor activity, relative to control transplanted MitoPark mice. Our results suggest that disinhibition of the Akt-signalling pathway may provide a valuable strategy to enhance survival, function and integration of grafted dopamine neurons within the host striatum and, more generally, to improve survival and integration of different forms of neural grafts.

Immortalization of neuronal progenitors using SV40 large T antigen and differentiation towards dopaminergic neurons

Transplantation is common in clinical practice where there is availability of the tissue and organ. In the case of neurodegenerative disease such as Parkinson's disease (PD), transplantation is not possible as a result of the non-availability of tissue or organ and therefore, cell therapy is an innovation in clinical practice. However, the availability of neuronal cells for transplantation is very limited. Alternatively, immortalized neuronal progenitors could be used in treating PD. The neuronal progenitor cells can be differentiated into dopaminergic phenotype. Here in this article, the current understanding of the molecular mechanisms involved in the differentiation of dopaminergic phenotype from the neuronal progenitors immortalized with SV40 LT antigen is discussed. In addition, the methods of generating dopaminergic neurons from progenitor cells and the factors that govern their differentiation are elaborated. Recent advances in cell-therapy based transplantation in PD patients and future prospects are discussed.

Dopamine cell transplantation for Parkinson's disease: the importance of controlled clinical trials

Transplantation of human fetal dopamine neurons into the brain of Parkinson's disease patients started in the late 1980s, less than 10 years after experiments in rats showed that embryonic dopamine neurons from a narrow window of development are suitable for transplantation. For human transplantation, the critical stage of development is 6 to 8 weeks after conception. Because putamen is the basal ganglia structure most depleted of dopamine in Parkinson's disease and because it is the structure most closely mapped to the motor cortex, it has been the primary target for neurotransplantation. The double blind trial conducted at the University of Colorado, Columbia University, and North Shore University is the first controlled surgical trial performed in the field of neurosurgery. Results have shown that transplants of fetal dopamine neurons can survive transplantation without immunosuppression and without regard to the age of the patients. Transplants improved objective signs of Parkinson's disease to the best effects of L-DOPA seen preoperatively. Placebo surgery produced no clinical changes. In subjects in whom transplants replaced the need for L-DOPA, the implants replicated the preoperative effects of L-DOPA, including dyskinesias in susceptible patients. Our trial has provided the first controlled evidence that dopamine cell transplants can improve the clinical state of patients with Parkinson's disease.

Cell transplantation and gene therapy in Parkinson's disease

Parkinson's disease is a progressive neurodegenerative disorder affecting, in part, dopaminergic motor neurons of the ventral midbrain and their terminal projections that course to the striatum. Symptomatic strategies focused on dopamine replacement have proven effective at remediating some motor symptoms during the course of disease but ultimately fail to deliver long-term disease modification and lose effectiveness due to the emergence of side effects. Several strategies have been experimentally tested as alternatives for Parkinson's disease, including direct cell replacement and gene transfer through viral vectors. Cellular transplantation of dopamine-secreting cells was hypothesized as a substitute for pharmacotherapy to directly provide dopamine, whereas gene therapy has primarily focused on restoration of dopamine synthesis or neuroprotection and restoration of spared host dopaminergic circuitry through trophic factors as a means to enhance sustained controlled dopamine transmission. This seems now to have been verified in numerous studies in rodents and nonhuman primates, which have shown that grafts of fetal dopamine neurons or gene transfer through viral vector delivery can lead to improvements in biochemical and behavioral indices of dopamine deficiency. However, in clinical studies, the improvements in parkinsonism have been rather modest and variable and have been plagued by graft-induced dyskinesias. New developments in stem-cell transplantation and induced patient-derived cells have opened the doors for the advancement of cell-based therapeutics. In addition, viral-vector-derived therapies have been developed preclinically with excellent safety and efficacy profiles, showing promise in clinical trials thus far. Further progress and optimization of these therapies will be necessary to ensure safety and efficacy before widespread clinical use is deemed appropriate.

Dopamine cell transplantation in Parkinson's disease: challenge and perspective

BACKGROUND

Functional imaging provides a valuable adjunct to clinical evaluation for assessing the efficacy of cell-based restorative therapies in Parkinson's disease (PD).

SOURCES OF DATA

In this article, we review the latest advances on the use of positron emission tomography (PET) imaging in evaluating the surgical outcome of embryonic dopamine (DA) cell transplantation in PD patients.

AREAS OF AGREEMENT

These studies suggest long-term cell survival and clinical benefit following striatal transplantation of fetal nigral tissue in PD patients and in models of experimental parkinsonism.

AREAS OF CONTROVERSY

Adverse events subsequent to transplantation have also been noted and attributed to a variety of causes.

GROWING POINTS

Optimal outcomes of DA cell transplantation therapies are dependent on tissue composition and phenotype of DA neurons in the graft.

AREAS TIMELY FOR DEVELOPING RESEARCH

Given continued progress in DA neuron production from stem cells in recent years, transplantation of neural stem cells may be the next to enter clinical trials in patients.

CONCLUSION

The existing data from studies of embryonic DA transplantation for advanced PD have provided valuable insights for the design of new cell-based therapies for the treatment of this and related neurodegenerative disorders.

Neural grafting in Parkinson's disease unraveling the mechanisms underlying graft-induced dyskinesia

The development of neural transplantation as a treatment for Parkinson's disease has been compromised by a lack of functional efficacy and the appearance of transplant-induced motor side-effects in some patients. Since the first reports of these graft-induced dyskinesias (GID), and the realization of their impact on the progress of the field, a great deal of experimental work has been performed to determine the underlying cause(s) of this problematic side-effect. In this review we describe the clinical phenomenon of GID, explore the different representations of GID in rodent models, and examine the various hypotheses that have been postulated to be the cause. Based on the available clinical and preclinical data we outline strategies to avoid GID in future clinical trials using fetal cell transplants or cell preparations derived from stem cells.

Neuronal cell replacement in Parkinson's disease

Transplantation of foetal dopamine neurons into the striatum of Parkinson's disease patients can provide restoration of the dopamine system and alleviate motor deficits. However, cellular replacement is associated with several problems. As with pharmacological treatments, cell therapy can lead to disabling abnormal involuntary movements (dyskinesias). The exclusion of serotonin and GABA neurons, and enrichment of substantia nigra (A9) dopamine neurons, may circumvent this problem. Furthermore, although grafted foetal dopamine neurons can survive in Parkinson's patients for more than a decade, the occurrence of Lewy bodies within such transplanted cells and reduced dopamine transporter and tyrosine hydroxylase expression levels indicate that grafted cells are associated with pathology. It will be important to understand if such abnormalities are host- or graft induced and to develop methods to ensure survival of functional dopamine neurons. Careful preparation of cellular suspensions to minimize graft-induced inflammatory responses might influence the longevity of transplanted cells. Finally, a number of practical and ethical issues are associated with the use of foetal tissue sources. Thus, future cell therapy is aiming towards the use of embryonic stem cell or induced pluripotent stem cell derived dopamine neurons.

Effects of GDNF pretreatment on function and survival of transplanted fetal ventral mesencephalic cells in the 6-OHDA rat model of Parkinson's disease

Transplantation of fetal dopaminergic (DA) neurons offers an experimental therapy for Parkinson's disease (PD). The low availability and the poor survival and integration of transplanted cells in the host brain are major obstacles in this approach. Glial cell line-derived neurotrophic factor (GDNF) is a potent neurotrophic factor with growth- and survival-promoting capabilities for developing DA neurons. In the present study, we examined whether pretreatment of ventral mesencephalic (VM) free-floating roller tube (FFRT) cultures with GDNF would improve graft survival and function. For that purpose organotypic cultures of E14 rat VM were grown for 2, 4 or 8 days in the absence (control) or presence of GDNF [10 ng/ml] and transplanted into the striatum of 6-hydroxydopamine-lesioned rats. While all groups of rats showed a significant reduction in d-amphetamine-induced rotations at 6 weeks posttransplantation a significantly improved graft function was observed only in the days in vitro (DIV) 4 GDNF pretreated group compared to the control group. In addition, no statistical significant differences between groups were found in the number of surviving tyrosine hydroxylase-immunoreactive (TH-ir) neurons assessed at 9 weeks posttransplantation. However, a tendency for higher TH-ir fiber outgrowth from the transplants in the GDNF pretreated groups as compared to corresponding controls was observed. Furthermore, GDNF pretreatment showed a tendency for a higher number of GIRK2 positive neurons in the grafts. In sum, our findings demonstrate that GDNF pretreatment was not disadvantageous for transplants of embryonic rat VM with the FFRT culture technique but only marginally improved graft survival and function.

Prospects of stem cell therapy for replacing dopamine neurons in Parkinson's disease

In Parkinson's disease (PD), the main pathology is a loss of nigrostriatal dopamine (DA) neurons. Clinical trials with intrastriatal transplantation of human embryonic mesencephalic tissue have shown that grafted DA neurons reinnervate the striatum, restore striatal DA release and, in some patients, induce major clinical benefit. Stem cells could provide an unlimited source of DA neurons for transplantation. Recent studies demonstrate that cells with properties of mesencephalic DA neurons can be produced from stem cells of different sources including reprogrammed somatic cells. However, as we discuss here, it remains to be shown that these cells can provide efficient functional reinnervation and behavioral recovery in animal PD models. Moreover, a clinically competitive cell therapy for PD will require better criteria for patient selection, improved functional efficacy of grafts by a tailor-made transplantation procedure providing optimum repair of the patient's DA system and strategies to prevent dyskinesias and tumor formation.

GDNF therapy for Parkinson's disease

With an increase in the aging population, the incidence of Parkinson's disease (PD), a disabling neurodegenerative disorder mainly affecting motor function, will inevitably present a challenge to an already overburdened healthcare system. Current medical and surgical therapies offer symptomatic relief but do not provide a cure. Experimental studies suggest that GDNF has the ability to protect degenerating dopamine neurons in PD as well as promote regeneration of the nigrostriatal dopamine system. However, clinical trials of GDNF infusion to date remain inconclusive. This review will examine the experimental and clinical evidence of GDNF use in PD with particular focus on its potential as an effective therapy in the treatment of PD.

Emerging restorative treatments for Parkinson's disease

Several exciting approaches for restorative therapy in Parkinson's disease have emerged over the past two decades. This review initially describes experimental and clinical data regarding growth factor administration. We focus on glial cell line-derived neurotrophic factor (GDNF), particularly its role in neuroprotection and in regeneration in Parkinson's disease. Thereafter, we discuss the challenges currently facing cell transplantation in Parkinson's disease and briefly consider the possibility to continue testing intrastriatal transplantation of fetal dopaminergic progenitors clinically. We also give a more detailed overview of the developmental biology of dopaminergic neurons and the potential of certain stem cells, i.e. neural and embryonic stem cells, to differentiate into dopaminergic neurons. Finally, we discuss adult neurogenesis as a potential tool for restoring lost dopamine neurons in patients suffering from Parkinson's disease.

Therapeutic potentials of human embryonic stem cells in Parkinson's disease

The loss of dopaminergic neurons of the substantia nigra is the pathological hallmark characteristic of Parkinson's disease (PD). The strategy of replacing these degenerating neurons with other cells that produce dopamine has been the main approach in the cell transplantation field for PD research. The isolation, differentiation, and long-term cultivation of human embryonic stem cells and the therapeutic research discovery made in relation to the beneficial properties of neurotrophic and neural growth factors has advanced the transplantation field beyond dopamine-producing cells. The present review addresses recent advances in human embryonic stem cell experimentation in relation to treating PD, as well as cell transplantation techniques in conjunction with alternative therapeutics.

Survival, differentiation, and migration of bioreactor-expanded human neural precursor cells in a model of Parkinson disease in rats

Object

Fetal tissue transplantation for Parkinson disease (PD) has demonstrated promising results in experimental and clinical studies. However, the widespread clinical application of this therapeutic approach is limited by a lack of fetal tissue. Human neural precursor cells (HNPCs) are attractive candidates for transplantation because of their long-term proliferation activity. Furthermore, these cells can be reproducibly expanded in a standardized fashion in suspension bioreactors. In this study the authors sought to determine whether the survival, differentiation, and migration of HNPCs after transplantation depended on the region of precursor cell origin, intracerebral site of transplantation, and duration of their expansion.

Methods

Human neural precursor cells were isolated from the telencephalon, brainstem, ventral mesencephalon, and spinal cord of human fetuses 8–10 weeks of gestational age, and their differentiation potential characterized in vitro. After expansion in suspension bioreactors, the HNPCs were transplanted into the striatum and substantia nigra of parkinsonian rats. Histological analyses were performed 7 weeks posttransplantation.

Results

The HNPCs isolated from various regions of the neuraxis demonstrated diverse propensities to differentiate into astrocytes and neurons and could all successfully expand under standardized conditions in suspension bioreactors. At 7 weeks posttransplantation, survival and migration were significantly greater for HNPCs obtained from the more rostral brain regions. The HNPCs differentiated predominantly into astrocytes after transplantation into the striatum or substantia nigra regions, and thus no behavioral improvement was observed.

Conclusions

Understanding the regional differences in HNPC properties is prerequisite to their application for PD cell restoration strategies.

Adjunctive use of the non-ionic surfactant Poloxamer 188 improves fetal dopaminergic cell survival and reinnervation in a neural transplantation strategy for Parkinson's disease

Although neural transplantation of fetal dopaminergic cells is a promising therapy for Parkinson's disease, poor transplanted cell survival limits its efficacy. In the present study it was hypothesized that the use of Poloxamer 188 (P188), a non-ionic surfactant, during cell preparation and transplantation may protect cells from associated mechanical injury and thus improve transplanted cell survival in a rat model of Parkinson's disease. Fetal rat dopaminergic tissue was dissociated in media with or without P188 and then cultured for 1 week or transplanted into the striatum of rats with unilateral 6-hydroxydopamine lesions of the nigrostriatal dopaminergic pathway. Fetal dopaminergic cell survival and reinnervation of the host brain were examined using tyrosine hydroxylase immunohistochemistry and stereological quantification. The number of surviving tyrosine hydroxylase-immunoreactive cells in vitro and in vivo was significantly increased by 2.2-fold by incubating fetal dopaminergic cells with P188 during tissue dissociation. Furthermore, the striatal reinnervation in parkinsonian rats that received intrastriatal transplants of P188-exposed dopaminergic cells was significantly enhanced (1.8-fold increase) compared with rats that received non-P188-treated cells. In conclusion, P188 protects fetal dopaminergic cells from mechanical injury by increasing cell survival and enhances dopaminergic fibre outgrowth into the transplanted striatum. Use of P188 may thus be an important adjunct to improve the clinical efficacy of neural transplantation for Parkinson's disease.

From bench to bed: the potential of stem cells for the treatment of Parkinson's disease

Parkinson's disease (PD) is the most common movement disorder. The neuropathology is characterized by the loss of dopamine neurons in the substantia nigra pars compacta. Transplants of fetal/embryonic midbrain tissue have exhibited some beneficial clinical effects in open-label trials. Neural grafting has, however, not become a standard treatment for several reasons. First, the supply of donor cells is limited, and therefore, surgery is accompanied by difficult logistics. Second, the extent of beneficial effects has varied in a partly unpredictable manner. Third, some patients have exhibited graft-related side effects in the form of involuntary movements. Fourth, in two major double-blind placebo-controlled trials, there was no effect of the transplants on the primary endpoints. Nevertheless, neural transplantation continues to receive a great deal of interest, and now, attention is shifting to the idea of using stem cells as starting donor material. In the context of stem cell therapy for PD, stem cells can be divided into three categories: neural stem cells, embryonic stem cells, and other tissue-specific types of stem cells, e.g., bone marrow stem cells. Each type of stem cell is associated with advantages and disadvantages. In this article, we review recent advances of stem cell research of direct relevance to clinical application in PD and highlight the pros and cons of the different sources of cells. We draw special attention to some key problems that face the translation of stem cell technology into the clinical arena.

The functional impact of the intrastriatal dopamine neuron grafts in parkinsonian rats is reduced with advancing disease

Clinical trials involving intrastriatal transplants of human embryonic mesencephalic tissue have provided proof-of-principle that nigral dopamine (DA) neurons can survive and functionally integrate into the host neural circuitry. However, the degree of graft-induced symptomatic relief differs significantly between the patients. This variability has led to investigations aimed at identifying factors that could affect the clinical outcome. The extent and pattern of dopaminergic denervation in the brain may be one of the major determinants of the functional outcome after intrastriatal DA cell grafts. Here, we report that in animals subjected to an intrastriatal 6-hydroxydopamine lesion of the striatal dopaminergic afferent, the integrity of the host dopaminergic innervation outside the areas innervated by the graft is critical for optimal function of DA neurons placed in the striatum. Established graft-induced functional recovery, as assessed in the stepping and cylinder tests, was compromised in animals in which the dopaminergic lesion was extended to include also the medial and ventral striatum as well as the cortical and limbic DA projections. Poor clinical outcome after transplantation may, thus, at least in part, be caused by dopaminergic denervation in areas outside the graft-innervated territories, and similarly beneficial effects initially observed in patients may regress if the degeneration of the host extrastriatal DA projection systems proceeds with advancing disease. This would have two implications: first, patients with advanced disease involving the ventral striatum and/or nonstriatal DA projections would be unlikely to respond well to intrastriatal DA grafts and, second, to retain the full benefit of the grafts, progression of the disease should be avoided by, for example, combining cell therapy with a neuroprotective approach.

Delivery of sonic hedgehog or glial derived neurotrophic factor to dopamine-rich grafts in a rat model of Parkinson's disease using adenoviral vectors Increased yield of dopamine cells is dependent on embryonic donor age

The poor survival of dopamine grafts in Parkinson's disease is one of the main obstacles to the widespread application of this therapy. One hypothesis is that implanted neurons, once removed from the embryonic environment, lack the differentiation factors needed to develop the dopaminergic phenotype. In an effort to improve the numbers of dopamine neurons surviving in the grafts, we have investigated the potential of adenoviral vectors to deliver the differentiation factor sonic hedgehog or the glial cell line-derived neurotrophic factor GDNF to dopamine-rich grafts in a rat model of Parkinson's disease. Adenoviral vectors containing sonic hedgehog, GDNF, or the marker gene LacZ were injected into the dopamine depleted striatum of hemiparkinsonian rats. Two weeks later, ventral mesencephalic cell suspensions were prepared from embryos of donor ages E12, E13, E14 or E15 and implanted into the vector-transduced striatum. Pre-treatment with the sonic hedgehog vector produced a three-fold increase in the numbers of tyrosine hydroxylase-positive (presumed dopaminergic) cells in grafts derived from E12 donors, but had no effect on E13-E15 grafts. By contrast, pre-treatment with the GDNF vector increased yields of dopamine cells in grafts derived from E14 and E15 donors but had no effect on grafts from younger donors. The results indicate that provision of both trophic and differentiation factors can enhance the yields of dopamine neurons in ventral mesencephalic grafts, but that the two factors differ in the age and stage of embryonic development at which they have maximal effects.